A wafer of semiconductor material (e.g. monocrystalline silicon) is subjected to multiple physiochemical treatments prior to becoming an electronic component (transistor, integrated circuit, etc.).
These treatments are performed in closed enclosures so as to take place under strictly controlled atmospheres, and in particular in the absence of any dust.
Workpieces need to be transferred from one enclosure to another using a moving enclosure, but without breaking the confinement and without running any risk of contamination.
it is easy to place a workpiece in a controlled atmosphere by using air-tight doors (with gaskets that are clamped).
It is also easy to transfer a workpiece from a fixed enclosure to a moving enclosure after docking the moving enclosure to the fixed enclosure, locking the enclosures together, clamping air-tight gaskets between them, and then opening separating doors.
Experience shows that all sorts of mechanical solutions are good at ensuring that the workpieces remain in a controlled atmosphere, but that they are disastrous when it comes to dust pollution.
Any air-tight door presupposes a gasket which is compressed, including friction and mechanical clamping, all of which operations generate dust. Opening the doors after docking is an even more pernicious operation since when the door is opened, the outside of the door moves into the inside the enclosure.